A very large percentage of all cancerous disease which spreads, or metastasizes, results in growth of metastatic tumors, called metastases, in the bony structures of the patient's body. In advanced metastatic bone disease, the patient experiences excruciating pain due to pressure of the tumor on surrounding nerves, tissue, and the innervation of the bone and endosteum or periosteum itself. The quality of the patient's life at this point can deteriorate quickly, and the levels of pain become intolerable.
The common methods of treating metastatic cancerous tumors include radiation therapy. Application of X-ray radiation therapy can slow the progression of bone metastatic cancer growth but usually cannot halt it. Moreover, some bone metastases are relatively unresponsive to radiation therapy. Another problem with radiation therapy is that it causes death of the bone marrow which produces the red blood cells that are vital to life. Therefore, only a limited amount of X-ray dosage can be given before critical destruction of bone marrow takes place. Another limitation of radiation therapy is that once it has been administered up to a certain dose level, further application of the radiation therapy typically is prohibited. This is to prevent overdosing of the surrounding normal tissue and organs in the patient. In sum, radiation therapy has a limited repeatability.
Radiation therapy also is a relatively complex and expensive procedure. Localization of the cancerous tumor with respect to the therapeutic X-ray beam may be difficult as a result of inaccurate patient positioning on an X-ray delivery device such as a linear accelerator (LINAC). To be effective, fractionated or repeated doses of radiation have to be given over a period of weeks or months. This is expensive in terms of equipment time and personnel costs, and can be inconvenient for a patient who is ill.
Localization of the metastatic tumor volume in the X-ray beam is a difficult technical problem which remains a challenge for radiation therapy. As a consequence of the indefiniteness of the tumor localization in the X-ray beam, larger margins of dosimetry must be given. This further puts at risk sensitive, normal tissue or organs that are nearby the bone and the bone tumor. Excess delivery of radiation to normal tissue can be very harmful with severe side effects and deterioration of the patient's condition and quality of life.
Chemotherapy is another method of treating bone metastases. This is a systemic treatment that can cause severe sickness in and inconvenience to the patient. Because of the toxicity of chemotherapy, the rest of the body's systems are put at risk. Moreover, the effectiveness of chemotherapy in targeting the bone tumor itself is limited.
The treatment of a primary benign bone tumor using a percutaneously placed radiofrequency electrode has been reported by Rosenthal, et al. in their paper entitled “Percutaneous Radiofrequency Treatment of Osteoid Osteomas,” Seminars in Masculoskeletal Radiology, Volume 1, Nov. 2, 1997. A radiofrequency electrode was inserted into the small primary bone tumor and connected to a radiofrequency power source to heat the bone tumor so as to destroy it. A bone tumor which they destroyed was of a type called “osteo-osteoma,” which is a relatively rare disease. They were successful in heating the osteo-osteoma tumor and destroying it completely in some cases. Osteo-osteomas are typically small tumors with a diameter of 1 to 2 centimeters. Rosenthal did not contemplate treating larger bone cancer or the painful condition they create.
It should be recognized that the theory behind and practice of radiofrequency (RF) heat lesioning has been known for decades, and a wide range of RF generators and electrodes for accomplishing such practice exist. For example, equipment for performing heat lesions is available from Radionics, Inc., located in Burlington, Mass. Radiofrequency (RF) ablation is well known and is described in medical and clinical literature. To that end, a research paper by E. R. Cosman, et al., entitled “Theoretical Aspects of Radiofrequency Lesions in the Dorsal Root Entry Zone,” Neurosurgery, Vol. 15; No. 6, pp. 945-950 (1984), describing various techniques associated with radiofrequency lesions, is incorporated herein by reference. Also, by reference, a research paper by S. N. Goldberg, et al., entitled “Tissue Ablation with Radiofrequency: Effective Probe Size, Gauge, Duration, and Temperature on Lesion Volume,” Acad. Radiol., Vol. 2; pp. 399-404 (1995), describes techniques and considerations relating to tissue ablation with radiofrequency energy.
In addition, a paper by S. N. Goldberg, et al., entitled “Hepatic Metastases: Percutaneous Radiofrequency Ablation with Cool-Tip Electrodes,” Radiology, Vol. 205, No. 2, pp. 367-373 (1997), describes various techniques and considerations relating to tissue ablation with radiofrequency electrodes having cooled electrode tips. Cooling of the electrode can result in larger volume of RF heating due to the extension of the heating volume to greater radii away from the electrode. Cooled ablation electrodes may maintain tissue near the electrode at temperatures that are below tissue ablation temperatures.